Oscillators – Relaxation oscillators
Reexamination Certificate
1999-07-29
2001-04-03
Pascal, Robert (Department: 2817)
Oscillators
Relaxation oscillators
C331S111000, C327S131000
Reexamination Certificate
active
06211746
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an integration method and integration circuit widely adopted for electronic circuits, and a voltage-controlled oscillator adopted widely for electronic circuits and to a frequency-voltage converter employing the integration circuit. More particularly, this invention is concerned with an integration method and integration circuit suitable for applications in which a variation in a factor relevant to charging or discharging an integrating capacitor falls within a predetermined narrow range. This invention is also concerned with a voltage-controlled oscillator and frequency-voltage converter employing the integration circuit.
2. Description of the Related Art
An integration circuit is widely adopted as part of an electronic circuit. When supply of a direct current to an integrating capacitor is started, a terminal voltage or a voltage developed at a terminal of the integration circuit rises with the passage of time. Assuming that a current is I, the terminal voltage is Vc, the capacitance of the integrating capacitor is C, and an integration time is T, the relationship of Vc=(I/C)×T is established. Herein, C is a fixed value.
When the integration circuit is used as part of an electronic circuit, the above relationship is utilized. One of I, T, and Vc is set to a predetermined value, and another one thereof is varied. A variation in the remaining one is detected. For example, the integration circuit may be used as part of a voltage-controlled oscillator. In this case, two reference voltages are determined, and the current I is varied proportionally to a voltage for inducing charge. When Vc reaches a first (higher) reference voltage, an output signal is varied. At the same time, the current I is varied for inducing discharge. When Vc reaches the second (lower) reference voltage, the output signal is varied. The current I is varied for inducing charge again. Thus, the output signal oscillates at a frequency dependent on a voltage.
In this kind of voltage-controlled oscillator, for example, a noise may be superposed on a reference voltage. In this case, a discharge period during which an integrating capacitor is discharged becomes unstable. This causes jitter in the output signal, and poses a problem in that a high-precision oscillating signal cannot be produced. As long as the magnitude of the noise is unchanged, the jitter relates to the ratio of the current I to the capacitance C, I/C. To reduce the jitter, the ratio I/C must be raised, and a change rate at which the terminal voltage of the integral capacitance makes a transition must be raised. However, the integration time is determined with the cycle of the oscillating signal. A difference between the two reference voltages cannot be increased. Consequently, it is impossible to raise the ratio I/C.
Moreover, a frequency-voltage converter employs the integration circuit as part of an electronic circuit. An input signal is, for example, a zero-crossing signal. When the input signal crosses a zero level, a pulsating signal is generated. The pulsating signal is used to reset the integration circuit. A terminal voltage or a voltage developed at a terminal of the integration circuit is sampled and held. An output signal is then produced based on the terminal voltage.
In the frequency-voltage converter, if a change rate at which the frequency of an input signal changes is low, a change rate at which the voltage level of an output signal changes is also low. This poses a problem in that the output signal is susceptible to a noise and the frequency-voltage converter suffers from a poor signal-to-noise ratio in terms of the output signal. To solve this problem, the ratio I/C of the current I to the capacitance C should be increased, and the change rate at which the terminal voltage Vc of the integrating capacitor makes a transition should be raised. When I/C is raised, Vc exceeds a voltage level that can be sampled and held. This is a problem and I/C cannot therefore be raised.
As mentioned above, as far as a circuit employing the integration circuit is concerned, it is preferred to raise the ratio I/C of a current to a capacitance for minimizing the influence of a noise. In practice, however, there is difficulty in raising I/C.
SUMMARY OF THE INVENTION
An object of the present invention is to realize an integration method and integration circuit capable of substantially raising the ratio I/C of a current to a capacitance. Moreover, an object of the present invention is to realize a voltage-controlled oscillator employing the integration circuit for reducing jitter, and a frequency-voltage converter offering a high signal-to-noise ratio.
In the integration method and integration circuit of the present invention, integration is suspended. The present inventor has directed his/her attention to the fact that factors relevant to charge or discharge of the integration circuit, that is, a charging or discharging current, a reference voltage or detection voltage, and a time vary within a limited range. A period during which integration is suspended falls within a range of variations in the time required by one integration. If the end of integration can be detected, although integration is suspended, necessary actions can be carried out. Moreover, an integration time is substantially shortened. Consequently, the ratio I/C of a current to a capacitance can be raised substantially.
In other words, an integration method in accordance with the present invention comprises a charge step at which an integrating capacitor is charged and a voltage detection step at which a voltage developed at the integrating capacitor is detected. The charge step includes a current supply step at which a current is supplied to the integrating capacitor and a stop step at which charge of the integrating capacitor is stopped during a predetermined period.
An integration circuit in accordance with the present invention comprises an integrating capacitor, a current source, a switch, a detection circuit, and a control circuit. The current source supplies a current to the integrating capacitor. The switch is installed on a path along which a current is supplied from the current source to the integrating capacitor. The detection circuit detects a voltage developed at the integrating capacitor. The control circuit controls the switch so that a current will be supplied from the current source to the integrating capacitor during an integration period. The integration period falls into a current supply period and a stop period. The control circuit controls the switch so that a current will be supplied from the current source to the integrating capacitor during the current supply period, and no current will be supplied from the current source to the integrating capacitor during the stop period.
The stop period during which current supply is stopped may be set in the middle of the integration period or at the start thereof. However, it is required that the end of integration can be detected. Moreover, the stop period during which current supply is stopped must be exactly constant but may be variable.
A voltage-controlled oscillator in accordance with the present invention comprises an integrating capacitor, a charge/discharge circuit, a reference level source, a comparison circuit, and a control circuit. The charge/discharge circuit charges or discharges the integrating capacitor using a current proportional to the voltage level of an input signal. The reference level source selectively outputs a first reference level and second reference level. The comparison circuit compares a voltage developed at the integrating capacitor with a reference level output from the reference level source, and outputs the results of comparison in the form of an oscillating signal. The control circuit controls charge and discharge of the integrating capacitor by the charge/discharge circuit. The reference level source outputs alternately the first and second reference levels in response to the oscillatin
Gotoh Kunihiko
Segawa Yuji
Armstrong, Westerman Hattori, McLeland & Naughton
Choe Henry
Fujitsu Limited
Pascal Robert
LandOfFree
Integration method and integration circuit offering improved... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Integration method and integration circuit offering improved..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Integration method and integration circuit offering improved... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2491595